The invention relates to a voltage monitoring system for a fuel cell stack.
A fuel cell is an electrochemical device that converts chemical energy produced by a reaction directly into electrical energy. For example, one type of fuel cell includes a proton exchange membrane (PEM), often called a polymer electrolyte membrane, that permits only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is reacted to produce hydrogen protons that pass through the PEM. The electrons produced by this reaction travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the hydrogen protons to form water. The anodic and cathodic reactions are described by the following equations:
H2xe2x86x922H++2exe2x88x92 at the anode of the cell, and
O2+4H++4exe2x88x92xe2x86x922H2O at the cathode of the cell.
A typical fuel cell has a terminal voltage near one volt DC. For purposes of producing much larger voltages, several fuel cells may be assembled together to form a fuel cell stack, an arrangement in which the fuel cells are electrically coupled together in series to form a larger DC voltage (a voltage near 100 volts DC, for example) and to provide more power.
The fuel cell stack may include flow plates (graphite composite or metal plates, as examples) that are stacked one on top of the other, and each plate may be associated with more than one fuel cell of the stack. The plates may include various surface flow channels and orifices to, as examples, route the reactants and products through the fuel cell stack. Several PEMs (each one being associated with a particular fuel cell) may be dispersed throughout the stack between the anodes and cathodes of the different fuel cells.
The health of a fuel cell stack may be determined by monitoring the individual differential terminal voltages (herein called cell voltages) of the fuel cells. In this manner, a particular cell voltage may vary under load conditions and cell health over a range from xe2x88x921 volt to +1 volt. For purposes of monitoring the cell voltages, wires may be attached to the flow plates and extend to a circuit board that includes circuitry for scanning the cell voltages. In this manner, each cell is associated with two wires: a first wire that is attached to a flow plate associated with the cathode of the cell and a second wire that is attached to another flow plate that is associated with the anode of the cell. Therefore, a fuel cell stack may have a considerable number of wires extending from the stack to the circuit board. Such an arrangement increases the time to manufacture the fuel cell stack, as a connection must be formed between the end of each wire and a particular flow plate. Each stack-to wire connection is also subject to failure, and thus, the above-described arrangement may have reliability problems. Furthermore, the above-described arrangement may increase the overall size of the assembly.
Thus, there is a continuing need for an arrangement that addresses one or more of the problems that are stated above.
In an embodiment of the invention, an assembly includes a fuel cell stack, a substrate (a printed circuit board or a flexible circuit, as examples) that supports electrical contacts and an electrical bridge (an elastomeric connector, for example). The fuel cell stack provides cell voltages, and the bridge provides indications of the cell voltages to the electrical contacts. The clamp holds the electrical bridge in compression against the fuel cell stack to communicate indications of the cell voltages to the electrical contacts.
In another embodiment of the invention, an assembly includes a fuel cell stack, a circuit board, an elastomeric connector and a frame. The elastomeric connector contacts the stack to provide cell voltages of the stack to the circuit board. The frame holds the circuit board and positions the elastomeric connector between the fuel cell stack and the circuit board.
Advantages and other features of the invention will become apparent from the following description, from the drawing and from the claims.